A retaining wall is a structure that holds back soil or rock from a building, structure or area. Retaining walls prevent downslope movement or erosion and provide support for vertical or near-vertical grade changes. Right side is bottom, left side is top

A retaining wall is a structure that holds back soil or rock from a building, structure or area. Retaining walls prevent downslope movement or erosion and provide support for vertical or near-vertical grade changes.

Also consider one-sided cutting=*s if it lines a highway and isn't a man-made wall. They're more flexible (but slightly less accurate) if you're refining an established way which already has other aspects that rely on its direction, such as already being oneway=yes or cycleway:left=lane, that would need to change to incorporate barrier=retaining_wall's "right side is bottom, left side is top" convention.